package com.example.demo.utils;
import java.util.ArrayList;
import java.util.List;
/**
 * @author lyc
 * @date 2019/9/2.
 */
public class QueryHelper {

    //from子句
    private String fromClause = "";
    //where子句
    private String whereClause = "";
    //order by子句
    private String orderByClause = "";

    private List<Object> parameters;
    //排序顺序
    public static String ORDER_BY_DESC = "DESC";//降序
    public static String ORDER_BY_ASC = "ASC";//升序

    /**
     * 构造from 子句
     * @param clazz 实体类
     * @param alias 实体类对应的别名
     */
    public QueryHelper(Class clazz, String alias){
        fromClause = "FROM " + clazz.getSimpleName() + " " + alias;
    }

    /**
     * 构造where子句
     * @param condition 查询条件语句；例如：i.title like ?
     * @param params 查询条件语句中?对应的查询条件值；例如： %标题%
     */
    public void addCondition(String condition, Object... params){
        if (whereClause.length() > 1) {//非第一个查询条件
            whereClause += " AND " + condition;
        } else {//第一个查询条件
            whereClause += " WHERE " + condition;
        }

        //设置查询条件值到查询条件值集合中
        if(parameters == null){
            parameters = new ArrayList<Object>();
        }
        if(params != null){
            for(Object param: params){
                parameters.add(param);
            }
        }
    }

    /**
     * 构造order by子句
     * @param property 排序属性，如：i.createTime
     * @param order 排序顺序，如：DESC 或者 ASC
     */
    public void addOrderByProperty(String property, String order){
        if (orderByClause.length() > 1) {//非第一个排序属性
            orderByClause += "," + property + " " + order;
        } else {//第一个排序属性
            orderByClause = " ORDER BY " + property + " " + order;
        }
    }

    //查询hql语句
    public String getQueryListHql(){
        return fromClause + whereClause + orderByClause;
    }

    //查询统计数的hql语句
    public String getQueryCountHql(){
        return "SELECT COUNT(*) " + fromClause + whereClause;
    }

    //查询hql语句中?对应的查询条件值集合
    public List<Object> getParameters(){
        return parameters;
    }
}